The present invention pertains to a fuel feed pump for a heater, especially for an auxiliary heater or a parking heater of a motor vehicle, and in particular to a heater with a magnet coil, an armature and delivery piston as well as spring-loaded valves.
In fuel feed pumps of the above-described class with spring-loaded pump valves, the opening and closing of the valve consequently depends on the pressure conditions in the medium being delivered. A possible admission pressure in front of the pump correspondingly affects the flow rate. The flow rate increases with increasing admission pressure. In addition, the pressure conditions in the intake line act directly on the delivery piston in current fuel feed pumps. If the pressure becomes too high, the force of the spring and the magnet is no longer sufficient to move the piston.
If the pump is equipped with xe2x80x9ctruexe2x80x9d valves, an increasing admission pressure does not lead to a breakdown of the delivery. However, the pump is flooded because the spring-loaded pressure valves open already at very low pressures. In the case of stronger springs, the pump does not operate any longer without admission pressure, i.e., with a pressureless feed line because the force of the magnet is no longer sufficient for opening the pressure valve.
Based on the above-mentioned problems, the primary object of the present invention is to improve a fuel feed pump of the type described in the introduction such that a satisfactorily metered delivery of the fuel medium by means of simple measures is possible largely independently from the pressure conditions in the supply or intake line of the pump.
This basic object of the present invention is accomplished by a fuel feed pump with a fluid line and a piston/cylinder unit in communication with the fluid line. The unit divides the fluid line into an intake side and a discharge side. The piston/cylinder unit includes a pump piston. An intake valve piston is arranged at the intake side of the fluid line, and a discharge valve piston is arranged at the discharge side of the fluid line. A pump piston armature is connected to the pump piston of the piston/cylinder unit, an intake armature is connected to the intake valve piston, and a discharge armature is connected to the discharge valve piston.
A common magnetic coil generates an alternating magnetic field common to the intake armature, the discharge armature and the piston armature. The intake armature, the discharge armature and the piston armature being arranged and having pumping structure to cooperate with each other and with the common alternating magnetic field to pump fluid in the fluid line from the intake side to the discharge side.
The pistons and armatures are spring loaded to move to a default or rest position when the magnetic coil is currentless.
An important feature of the present invention is that the spring-loaded valves are an electrically controlled intake valve and an electrically controlled pressure valve and that a common magnet coil is provided for the armature of the delivery piston, the armature of the intake valve and the armature of the pressure valve.
The magnet coil, the intake valve, the delivery piston with the armature and the pressure valve are preferably accommodated in a housing as one assembly unit.
The formation of vapor bubbles is prevented or minimized if a continuous fuel channel, which is connected to the piston of the intake valve, to the delivery piston and to the piston of the pressure valve, is provided in the housing in an especially advantageous variant of the present invention. The pistons of the intake and pressure valves as well as the delivery piston have circumferential seals, so that the magnet coil, the armature and the compression springs are located in a fuel-free interior space of the housing. The coil is separated from the fuel channel as a result. Due to such an arrangement of the coil, the fuel does not reach the vicinity of the heat-releasing coil windings, which helps avoid the evaporation of the fuel.
Provisions are made, in particular, for the spring-loaded intake valve to be open and the spring-loaded pressure valve to be closed by the spring force in the currentless state of the magnet coil and for the spring-loaded delivery piston to be in its withdrawn suction stroke end position or inoperative position and for the intake valve to be closed and for the pressure valve to be opened against the spring force of the intake valve upon the application of a magnet coil current and for the delivery piston to perform the delivery stroke, where the intake valve closes and the pressure valve opens more rapidly than the delivery stroke movement of the delivery piston upon the application of the magnet coil current.
The intake valve closes and the pressure valve opens preferably simultaneously upon the application of a magnet coil current.
The opening of the intake valve and the closing of the pressure valve preferably takes place more rapidly than the suction stroke movement of the delivery piston during the operation of the pump, even during interruptions of the magnet coil current, Just as in the case of the application of a magnet coil current, the opening of the intake valve and the closing of the pressure valve can also take place simultaneously during an interruption of the magnet coil current.
The above-mentioned switching operation is accomplished in terms of design by the armature of the intake valve and the armature of the pressure valve being smaller than the armature of the delivery piston and/or especially by the piston of the intake valve and the piston of the pressure valve having a smaller cross section than the delivery piston and/or especially also by the pretension of the compression spring of the intake valve and the pretension of the compression spring of the pressure valve being lower than the pretension of the compression spring of the delivery piston.
A simpler design is obtained especially by the piston of the intake valve and the piston of the pressure valve having an equal cross section and/or by the armature of the intake valve and the armature of the pressure valve having an identical design.
The intake valve, the delivery piston and the pressure valve may be arranged in series along a straight fuel channel and may especially be located at equally spaced locations from one another.
The housing preferably has a flat upper cover and is parallelepipedic, and the magnet coil is essentially also parallelepipedic with a corresponding parallelepipedic interior space for receiving the armature.
The end of the piston of the pressure valve that faces away from the armature may be accommodated in a guided manner in a hole of the housing and have especially a through hole, which is the valve opening, and releases the pressure line to the heater in an alignment or interconnection to the fuel channel.
Consequently, it is proposed according to the present invention that the pump be equipped with two controlled valves. The same magnetic force acts on these valves as on the piston. However, since the valve cross section is selected to be markedly smaller than the cross section of the piston, the valves respond more rapidly, and the valves also operate at higher pressures. If the intake valve is closed and the pressure valve is open, the delivery piston, now uncoupled from the pressure conditions in the intake line, can perform its task.
A fuel feed pump according to the present invention is consequently suitable for pressurized feed lines. The level of the admission pressure is practically irrelevant. The opening and closing of the valves depends on the force of the magnet and the spring rather than on the prevailing pressure.
However, the pump according to the present invention can also be used in pressureless feed lines, namely, xe2x80x9cintake linesxe2x80x9d in the direct sense of the word, because the spring force of the delivery piston brings about the suction stroke with the pressure valve closed and the intake valve open and draws the fuel from the intake or feed line as a result.
It is novel and important that the stroke of the piston and the valve actuation are carried out with the same coil. This is associated with the advantage that it is possible to reduce the number of components and thus to save costs compared with three individual components according to the state of the art (two timing valves xe2x80x9cproper,xe2x80x9d one delivery unit). A system with a closed design can also be easily coordinated, because the pulse for the delivery stroke applies the same force to all components at exactly the same time.
Another improvement over the prior art is obtained by the fact that valve balls are no longer able to stick together, because these valve balls are eliminated altogether.